Polishing fluid, polishing method, semiconductor device and semiconductor device fabrication method

ABSTRACT

A polishing fluid comprising a distributed organic phase and a continuous aqueous phase, each phase comprising at least one complexing agent. The aqueous phase also having abrasive particles dispersed therein. Reaction products generated during polishing interact with the aqueous phase complexing agent to form water soluble metallic complexes, the water soluble metallic complexes diffuse to an organic/water interface where they release complexing agent molecules in the aqueous phase and generate metal ions which interact with the organic phase complexing agent to form organometallic complexes. Further disclosed is a polishing method, a semiconductor device and semiconductor device fabrication method utilizing the polishing fluid.

FIELD OF THE INVENTION

The invention relates to semiconductor devices and fabrication methods,and more particularly to polishing of device layers.

BACKGROUND OF THE INVENTION

Surface finishing in many arts may utilize polishing and/orplanarization. As used herein the term “polishing” shall includepolishing and/or planarization. Polishing is of particular importance inthe manufacturing of semiconductor devices. The concentration ofintegrated circuit components included on a semiconductor chip iscontinually increasing. Concentration may be increased by decreasingcomponent size. As component size decreases, surfaces on whichcomponents are formed should be increasingly smooth to produce desiredcomponent configurations and thereby reduce failure rates and increaseproduct yield. Therefore, the effectiveness of polishing fluids hassignificant impact on the quality of integrated circuits produced.

Semiconductor devices typically comprise multiple layers, throughoutwhich are incorporated integrated circuits. Integrated circuit featuresand components, which may vary in height, are typically created bylithographic processes on each layer. Height variations contained on onelayer may present themselves on subsequent layers creating nonplanarlayer surfaces. Such surface irregularities may be problematic inlithographic processes used to form additional circuit components.Therefore, it is desirable to perform lithographic processes only onsubstantially smooth, planar surfaces.

A typical semiconductor device fabrication lithographic process includesdepositing a radiation sensitive material or resist on a surface,exposing the resist to radiation through a mask to transfer a desiredpattern onto the surface, and developing the resist to reveal theexposed pattern. Typically, if a resist is deposited on an irregularsurface, it will have a corresponding irregularity. Such irregularitiesmay cause variations in a depth of focus across the device so thatpattern features may not be brought uniformly into sharp focus. Ifportions of the surface are not in focus, the pattern may not beaccurately transferred.

Additionally, surface irregularities may adversely affect deviceinterconnect reliability because metal layers deposited over a surfaceirregularity may acquire unwanted configurations. These configurationsmay cause undesirable current crowding in metal layers. For the abovereasons polishing is an important step in semiconductor devicefabrication processes.

Chemical-mechanical polishing (CMP) is a technique widely used in thefabrication of semiconductor devices. CMP is performed by introducing apolishing fluid or slurry between a workpiece surface and a polishingarticle and moving the article and device relative to one another. Theslurry generally comprises abrasive particles which may mechanically andchemically wear down unwanted surface irregularities. Additionalconstituents chemically react with the workpiece surface to smooth andplanarize it. A polishing article, such as a polishing pad may alsomechanically wear away surface irregularities.

CMP reaction products may become imbedded in the surface which is beingpolished, and may cause scratches, particle defects and impurities insurfaces. For example, during copper CMP, traces of copper and barriermetal may be seen in the oxide dielectric layer. Defects, scratches andimpurities may reduce the reliability of the device. It is known in theart to utilize chemical solutions such as hydrofluoric acid (HF) toclean a surface after CMP to reduce adverse effects of reactionproducts. Although generally helpful in removing reaction products, suchsolutions may etch away a portion of the layer that was polished.Additionally, planarity or smoothness may be degraded by such post-CMPprocesses because of step generations caused by dielectric oxideremoval. Furthermore, solutions such as HF used in copper CMP may attackbarrier films causing localized corrosion in copper trenches. Therefore,it is desirable to develop a polishing fluid and method that removereaction products from the surface being polished without damaging thepolished layer.

SUMMARY OF THE INVENTION

The invention relates to a polishing fluid and method for polishingparticularly useful in the fabrication of semiconductor devices. Furtherdisclosed is a semiconductor device and a method for fabricating asemiconductor device employing the polishing fluid.

The polishing fluid comprises a distributed organic phase and acontinuous aqueous phase, each comprising at least one complexing agent.The aqueous phase also has abrasive particles dispersed therein.Reaction products generated during polishing interact with thecomplexing agent in the aqueous phase to form water soluble metalliccomplexes. The water soluble metallic complexes diffuse to anorganic/water interface where they release complexing agent molecules inthe aqueous phase and form organometallic complexes in the organicphase, thereby substantially removing reaction products from the surfacebeing polished.

DESCRIPTION OF THE DIAGRAM

A cross-sectional view of a semiconductor device.

DETAILED DESCRIPTION OF THE INVENTION

It will be appreciated that the following description is intended torefer to specific embodiments of the invention selected for illustrationand is not intended to define or limit the invention, other than in theappended claims.

The polishing fluid of the invention comprises a distributed organicphase and a continuous aqueous phase. The organic phase is dispersed inthe continuous aqueous phase resulting in an oil-in-water type emulsionuseful, for example, as a CMP slurry. Advantageously the aqueous phaseand the organic phase contain one or more complexing agents whichfacilitate substantial removal of reaction products from a workpiecesurface. During polishing, complexing agents in the aqueous phaseinteract with reaction products to form water soluble metalliccomplexes. Reaction products are species removed from the workpiecesurface during polishing such as, for example, tungsten, copper,aluminum, titanium, silicon tungstenoxide, copperoxide, titaniumoxideand siliconoxide.

The general equation for the formation of the water soluble metalliccomplex is:

M+R=M*R

where M is a metal molecule, R is a complexing agent in the aqueousphase, and M*R is a water soluble metallic complex. The water solublemetallic complex diffuses to an organic/water interface where itundergoes a strip action releasing a complexing agent molecule in theaqueous phase and providing a metal ion, which may be expressed by:

M*R=M ⁺(aq)+R

This in effect transports the metal ion to the organic/water interfacewhere it interacts with a complexing agent in the organic phase, formingan organometallic complex. The general equation for the formation of theorganometallic complex is:

M ⁺(aq)+R′−OH=M−R′+H₂O

where R′—OH is a complexing agent in the organic phase and M−R′ is anorganometallic complex.

Once organometallic complexes are formed they generally remain in theorganic phase as polishing proceeds. Released complexing molecules inthe aqueous phase may subsequently complex with additional metallicspecies, continuing the process of complexing and stripping. Thisresults in an effective metal species transfer.

Additionally, selectivity of the polish slurry may be enhanced throughthis mechanism of carrier mediated transport of metal species to theorganic phase. Selectivity is enhanced by the selective complexation ofthe metal species with the addition of a chemical complexing agent inthe aqueous slurry. Typically the rates of chemical reactions forcomplexation and ligand regeneration are fast in such a transportprocess. Thus, the transport process is predominantly diffusion limited.The simultaneous complexation and metal stripping reactions generate asubstantially continuous chemical potential gradient for the transportto occur across the aqueous phase. Thus, by formation of water solublemetallic complexes at the organic/water interface and subsequentformation of organometallic complexes, reaction products aresubstantially removed and maintained away from a workpiece surface.Advantageously, removing and maintaining metals away from the workpiecesurface substantially eliminates possible detrimental effects posed bycontinued polishing with a reaction product-containing slurry.

A complexing agent in the aqueous phase may be any compound that wouldreact with metal ions in the aqueous phase to form water solublemetallic complexes. Preferred complexing agents include ethylenedi-amine tetra-acetic acid (EDTA) and di-ethylene tetra penta-aceticacid (DTPA). Combinations of complexing agents may also be used.

A complexing agent in the organic phase may be any compound that wouldreact with metal ions in the organic phase to form organometalliccomplexes. Diethylene-triamine-penta-acidic acid is generally aneffective complexing agent for any metal. For copper applicationsbipyridine or orthophenanthroline have been found to be particularlyeffective. 8-hydroxy-quinoline may be used as a complexing agent and hasbeen found to be particularly effective for slurries used to polishaluminum. Combinations of complexing agents may also be used.

The organic phase may advantageously be regenerated and reused foremulsion formation. After the polishing fluid has been utilized,organometallic complexes are dissolved in the organic phase. Theorganometallic complexes can be split from the organic phase toregenerate organic solvent. Regeneration may be performed by ionexchange or by dissolution in an acidic medium or any other method thatstrips the solvent of the organometallic complexes.

The aqueous phase contains abrasive particles which may mechanicallywear away material from a workpiece being polished and may also reactchemically with the surface material to further effect polishing.Abrasive particles preferably comprise about 5 weight percent to about30 weight percent of the polishing fluid. Examples of abrasives include,but are not limited to, ceria, alumina, silica, magnesium oxide andcombinations thereof These abrasives are particularly effective inchemical-mechanical polishing of semiconductor device layers.

The diameter of the abrasive particles is preferably in the range ofabout 100 nm to about 1000 nm, more preferably in the range of about 200nm to about 500 nm and most preferably in the range of about 300 nm toabout 400 nm. Particles may be any shape, with the “diameter” denotingroughly the longest dimensional line of the particle taken from onesurface point to another, through the particle midpoint. If particlesare too large, meaning greater than about 1100 nm, scratching of thesurface being polished may occur. Additionally, removal rates may be toohigh and, therefore, difficult to control or limit, and polishingresults may be less uniform.

The weight percent of solids contained in the slurry may affectpolishing results. For example, too high a weight percent of solids,generally greater than 50%, may cause scratching of the surface beingpolished, higher than desired removal rates or nonuniform polishing.Solids as used herein refer to abrasives, salts such as for exampleNH₄NO₃, stabilizers, abrasive agglomerates and any other componentpresent in a solid phase. The percent solids is preferably in the rangeof about 20 weight percent to about 50 weight percent of the polishingfluid.

The organic phase may contain additives to attain a particular pH, thedesired value of which is dependent on the slurry application. Additivesmay also be used to alter reaction characteristics to tailor thechemical potential gradient which transports metal species across theaqueous phase. Other components that may enhance polishing or improvecharacteristics of the polishing fluid, such as for example, to increaseshelf life or polishing uniformity, may also be added to the organicphase.

The aqueous phase may also include one or more of the followingconstituents: oxidants, emulsion stabilizers, surfactants, and acids oralkali components. Other components that may enhance polishing orimprove characteristics of the polishing fluid may also be added to theaqueous phase.

Oxidants may include, for example, NH₄OH, NH₄NO₃, H₂O₂ or mixturesthereof These components oxidize metal surfaces to enhance polishing.The oxides of metals such as for example, Ta, Ti, W and Al, are softerthan the pure metal and, therefore, are more easily polished. For somemetals, for example copper, oxidants also protect the surface fromcorrosion. An oxidized layer acts as a passivization layer that protectsthe bulk metal from corrosion. In this manner CMP and oxidation mayoccur simultaneously.

Emulsion stabilizers keep phases substantially uniformly dispersed andprotect the polishing fluid from degradation such as from fungal growth.Emulsion stabilizers may include, for example, sulfonates, but anyemulsion stabilizer that aids in substantially uniformly dispersing thephases or that protects against slurry degradation may be used, providedthat its benefits do not outweigh any negative effects on polishedsurfaces or to slurry polishing capabilities.

Surfactants may be utilized to aid in creating and maintaining thedistributed phase within the continuous phase. Surfactants comprisehydrophilic and hydrophobic groups allowing them to attract both thedistributed and continuous phases, thereby facilitating immiscibility.Surfactants may also improve the slurry's ability to wet the workpieceor polishing article. Surfactants may include, but are not limited to,alkyl, benzyl, lauryl sulfonates or combinations thereof.

Acids or alkali solutions may be added for pH control. The desired pH ofthe polishing fluid depends on the type of surface being polished. Forexample, a pH in the range of about 2 to about 6 is preferable whenpolishing metals, whereas a pH in the range of about 9 to about 13 ispreferable when polishing dielectrics which typically comprise oxides.Generally, in applications of the inventive slurry the pH is preferablybetween about 2 and about 6 and more preferably between about 3 andabout 5.

The ratio of the distributed phase to the continuous phase is preferablyin the range of about 2:98 volume percent to about 50:50 volume percentof the polishing fluid, and more preferably in the range of about 5:95volume percent to about 40:60 volume percent. The ratio of volumepercents of the distributed phase to the continuous phase in excess of50:50 may result in reversal of the distributed and the continuousphases. Therefore, to ensure the integrity of the slurry system, thevolume percent ratio should be maintained below 50:50.

The invention further includes a semiconductor device and fabricationmethod wherein at least some device layers are polished utilizing thepolishing fluid of the invention. Device performance and reliability isexpected to be improved due to the removal of reaction products fromsurfaces during polishing steps.

The drawing depicts a schematic of a semiconductor device 200. Thoseskilled in the art will understand that it shows a simplified drawing ofsemiconductor device 200 for illustrative purposes only. For example, anactual device may have layers of varying thicknesses and may containother components. Semiconductor substrate 202 is covered by a firstdielectric layer 204. Above first dielectric layer 204 is a first metallayer 206. Vias or interconnects 208, 210, 212 and 214 penetrate layer204 and conductively connect first metal layer 206 to semiconductorsubstrate 202. First metal layer 206 is covered by second dielectriclayer 216 which contains vias 218, 220 and 222 to connect first metallayer 206 to a second metal layer 224. This layering sequence may berepeated as necessary as shown in part by layers 226 and 228, andinterconnects 232, 234 and 236. A top passivation layer 230 may beapplied to protect device 200 from adverse electrical, chemical or otherconditions, and to provide electrical stability.

Semiconductor substrate 202 may comprise silicon for example. Commondielectrics include, but are not limited to, silicon oxides, such asboron phosphorous doped silicate glass (BPSG), tetraethylorthosilicate(TEOS) and silicon dioxide (SiO₂). Common metals include, for example,aluminum, copper and tungsten. In addition, to improve adherence betweenmetal and dielectric layers, thin layers may be introduced between them.Titanium is commonly used for this purpose. Electronic circuitry isdefined in the layers by a lithographic technique.

In the lithographic process used to form the circuitry in device 200 aresist is deposited over a device layer. The resist is exposed bytransmitting radiation through a mask or reticle onto the layer surface.The mask pattern defines the desired circuitry or other feature. Theform of radiation used is dependent on the type of resist and otherfabrication parameters. Any form of radiation that may expose the resistwithout adverse effects to the workpiece may be used. Common examplesinclude, ultraviolet radiation, electron beam radiation and x-rays. If apositive resist is used, the exposed areas will be removed revealing thedielectric layer below. The dielectric layer may then be removed, forexample by etching. Any technique that will remove the exposeddielectric layer while leaving the resist covered portions intact mayalso be used. Negative resists may be used wherein the exposed resistareas are left intact after exposure and the nonexposed areas areremoved. For negative resist processes a mask is used that defines thespaces between circuit components rather than the circuitry itself.Similar lithographic processes may also be employed to form theinterconnects in the dielectric layers or other device features.

Surfaces of some or all of the device layers may be polished duringdevice 200 fabrication to create a substantially smooth, planar surfacefor accurate transfer of circuit patterns and creation of circuitcomponents, and to satisfactorily carry out other fabrication steps.Surfaces are polished by bringing a polishing article in at leastpartial contact with the surface. The polishing fluid of the inventionis introduced between the semiconductor device surface being polishedand a polishing article. The semiconductor device surface and polishingarticle are effectively moved in relation to one another. This may beaccomplished by either moving the device or the polishing article inrelation to a polishing apparatus or moving both the device and thepolishing article in relation to one another. Once the layer is polishedit can undergo further processes if necessary to fabricate thesemiconductor device. Surfaces of any number of device layers may bepolished using the polishing fluid and method of the invention.

What is claimed is:
 1. A polishing fluid comprising a distributedorganic phase and a continuous aqueous phase, the aqueous phase havingat least one complexing agent selected from the group consisting ofdiethylene-tetra-penta-acidic acid, ethylene di-amine tetra acetic acidand a combination thereof and abrasive particles dispersed therein, andthe organic phase having at least one complexing agent, wherein reactionproducts generated during polishing interact with the aqueous phasecomplexing agent(s) to form water soluble metallic complexes, the watersoluble metallic complexes diffuse to an organic/water interface wherethey release complexing agent molecules in the aqueous phase andinteract with the organic phase complexing agent(s) to formorganometallic complexes in the organic phase.
 2. A polishing fluidcomprising a distributed organic phase and a continuous aqueous phase,the aqueous phase having at least one complexing agent and abrasiveparticles dispersed therein, and the organic phase having at least onecomplexing agent selected from the group consisting ofdiethylene-triamine-penta-acidic acid, bipyridine, orthophenanthroline,8-hydroxyquinoline and a combination thereof, wherein reaction productsgenerated during polishing interact with the aqueous phase complexingagent(s) to form water soluble metallic complexes, the water solublemetallic complexes diffuse to an organic/water interface where theyrelease complexing agent molecules in the aqueous phase and interactwith the organic phase complexing agent(s) to form organometalliccomplexes in the organic phase.
 3. A polishing fluid comprising adistributed organic phase and a continuous aqueous phase, the aqueousphase having at least one complexing agent, abrasive particles and oneor more components selected from the group consisting of 1) oxidantsselected from the group consisting of NH₄OH, NH₄NO₃, H₂O₂ and acombination thereof, 2) surfactants and 3) emulsion stabilizersdispersed therein, and the organic phase having at least one complexingagent, wherein reaction products generated during polishing interactwith the aqueous phase complexing agent(s) to form water solublemetallic complexes, the water soluble metallic complexes diffuse to anorganic/water interface where they release complexing agent molecules inthe aqueous phase and interact with the organic phase complexingagent(s) to form organometallic complexes in the organic phase.
 4. Apolishing fluid comprising a distributed organic phase and a continuousaqueous phase, the aqueous phase having at least one complexing agent,abrasive particles and one or more components selected from the groupconsisting of oxidants, surfactants selected from the group consistingof alkyl, benzyl, lauryl sulfonates and combinations thereof andemulsion stabilizers dispersed therein, and the organic phase having atleast one complexing agent, wherein reaction products generated duringpolishing interact with the aqueous phase complexing agent(s) to formwater soluble metallic complexes, the water soluble metallic complexesdiffuse to an organic/water interface where they release complexingagent molecules in the aqueous phase and interact with the organic phasecomplexing agent(s) to form organometallic complexes in the organicphase.
 5. A polishing fluid comprising a distributed organic phase and acontinuous aqueous phase, the aqueous phase having at least onecomplexing agent and abrasive particles selected from the groupconsisting of ceria, alumina, silica, magnesium oxide and combinationsthereof dispersed therein, and the organic phase having at least onecomplexing agent, wherein reaction products generated during polishinginteract with the aqueous phase complexing agent(s) to form watersoluble metallic complexes, the water soluble metallic complexes diffuseto an organic/water interface where they release complexing agentmolecules in the aqueous phase and interact with the organic phasecomplexing agent(s) to form organometallic complexes in the organicphase.